The present invention relates generally to an igniter for a gas turbine engine and, in particular, to an apparatus for positioning an igniter within the liner port of a gas turbine engine.
It is well known for a gas turbine engine to employ an igniter in order to ignite a fuel/air mixture within its combustion system and produce the desired gases. Typically, the igniter is positioned in relative proximity to the fuel/air mixture exiting a mixing device through a port in the outer liner, which results in the igniter being projected into an area defining the primary combustion zone downstream of the mixing device. While various improvements have been made to the igniter itself and the cooling thereof (e.g., U.S. Pat. No. 3,990,834 to DuBell et al.), it will be understood that little has been accomplished with respect to the apparatus maintaining the igniter in position within a port in the outer liner of the gas turbine engine combustor.
Current devices utilized for this purpose have evolved from a simple tube into a hollow tube having a flange on top to prevent the igniter tube from entering the combustor flow path. Such flange may either be part of the tube or a cap plate welded onto a simple tube. Other igniter tubes have been utilized in conjunction with ferrules that have wear collars which extend below the sealing surface. To date, however, such igniter tubes generally have a single bore inner diameter.
One concern that has recently come to the attention of those in the art is the ability to inspect the weld joint connecting the igniter tube to the liner port. In particular, it has been found that axial clearance between the igniter tube and a cooling nugget for the liner needed to be increased to allow a line of sight inspection of such weld joint. Current specifications dictate that a clearance of at least 0.100 of an inch be provided to permit inspection by florescent penetration.
Additionally, igniter tubes have not provided any mechanism for preventing liberation of the igniter tube into the combustor flowpath in the event of a weld failure. It will be appreciated that absent such a mechanism, the igniter tube will simply slide inboard until a flange contacts the liner. This can cause the tip of the igniter to be shrouded by the igniter tube, thereby preventing normal operation of the igniter.
Similarly, it has also been found that the sealing flange of a ferrule utilized with the igniter tube has the possibility of wearing through, whereby the ferrule is then able to enter the combustor flowpath. At the same time, the use of a low profile ferrule, where the wear collar is located below the sealing surface with the igniter tube, is encouraged in order to promote greater clearance to the combustor casing.
Thus, in light of the foregoing, it would be desirable for an improved igniter tube for a gas turbine engine to be developed which permits greater axial clearance for line of sight inspection of the weld joint retaining such igniter tube to a liner port. It would also be desirable for such igniter tube to permit use of a low profile ferrule while providing positive retention features which prevent the igniter tube and ferrule from entering the combustor flow path.
In a first exemplary embodiment of the invention, an igniter tube for a gas turbine engine combustor is disclosed as having an inner surface, an outer surface, and a longitudinal axis therethrough. More specifically, the igniter tube includes: a first portion positioned within a port of a liner for the combustor, the first portion having an inner surface with an inner diameter and an outer surface with an outer diameter; a second portion located adjacent the first portion, the second portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the second portion outer diameter increases from the first portion outer diameter at a first end to a predetermined outer diameter at a second end; and, a third portion located adjacent the second portion, the third portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the third portion outer diameter is substantially equal to the predetermined outer diameter. Moreover, the second portion inner diameter of the igniter tube is substantially equal to the first portion inner diameter and the third portion inner diameter of the igniter tube is greater than the inner diameter of the second portion.
In a second exemplary embodiment of the invention, an apparatus for positioning an igniter within a liner port of a gas turbine engine combustor is disclosed, wherein a longitudinal axis extends through the liner port. The apparatus includes a ferrule for receiving the igniter and an igniter tube connected to the liner port. The ferrule further includes a first portion, a wear collar extending from the first portion generally parallel to the longitudinal axis, and a sealing flange extending substantially perpendicular to the longitudinal axis. The igniter tube further includes: a first portion positioned within the liner port, the first portion having an inner surface with an inner diameter and an outer surface with an outer diameter; a second portion located adjacent the first portion, the second portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the second portion inner diameter is substantially equal to the first portion inner diameter; and, a third portion located adjacent the second portion, the third portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the third portion inner diameter is greater than the first and second portion inner diameters. The ferrule wear collar extends into the igniter tube third portion and is able to move substantially perpendicular to the longitudinal axis a predetermined amount.
In a third exemplary embodiment of the invention, an apparatus for positioning an igniter within a liner port of a gas turbine engine combustor is disclosed, wherein a longitudinal axis extends through the liner port. The apparatus includes a ferrule for receiving the igniter and an igniter tube connected to the liner port. The ferrule further includes a first portion, a wear collar extending from the upper portion generally parallel to the longitudinal axis, and a sealing flange extending substantially perpendicular to the longitudinal axis. The igniter tube further includes: a first portion positioned within the liner port, the first portion having an inner surface with an inner diameter and an outer surface with an outer diameter; a second portion located adjacent the first portion, the second portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the second portion outer diameter increases from the first portion outer diameter at a first end to a predetermined outer diameter at a second end; and, a third portion located adjacent the second portion, the third portion having an inner surface with an inner diameter and an outer surface with an outer diameter, wherein the third portion outer diameter is substantially equal to the predetermined outer diameter. The predetermined outer diameter of the second and third igniter tube portions is greater than a diameter of the liner port so as to prevent the igniter tube from extending therethrough past a predetermined distance.